Apparatus and methods of infrared signal processing for motion detectors

ABSTRACT

An apparatus and method of processing signals from a passive infrared sensor evaluates energy of received signals. An integration or accumulation process can be used to provide an indicator of signal energy. This indicator can be compared to a predetermined alarm threshold to determine if an alarm indication should be generated.

FIELD

The application pertains to surveillance systems for detecting anintruder in a monitored area of space, and particularly to the signalprocessing method for detectors. More specifically, it relates to amethod for the passive infrared signal recognition processing.

BACKGROUND

Motion detectors using passive infrared (PIR) technology are widely usedin the field of security. There are two key components in this type ofdetector, the one is a Fresnel lens array window which can focusinfrared energy produced by a heat source (such as human body) onto apyroelectric sensor that can convert the changes of infrared energyreaching it into an electrical signal; and the other is a pyroelectricsensor that can convert the infrared energy into an electrical signal.For example, if there is no motion heat source, then the sensor does notoutput characteristic signal (large amplitude changing randomly), and ifthere is a person walking in the monitoring area, then the sensordetects the temperature difference between the human body and thebackground, and output the corresponding characteristic signal.

The signals are amplified, sampled, and processed by hardware circuitand algorithms that determining whether there is an intruder or not, anda corresponding control output can be generated. Thus, in known PIRdetectors, the movement of a heat source is sensed. Some detectors, bycombing microwave technology with a PIR sensor, attempt to prevent falsealarms generated by only using the PIR technology.

A block diagram of a known PIR-type detector is illustrated in FIG. 1.The detector of FIG. 1 includes a PIR sensor module 110, an analogsignal processing module 120, a master controlling unit (MCU) module130. In the detector of FIG. 1 the sensor module outputs electricsignals in response to sensing the motion of a human body. The signalsare amplified by the analog circuit, and are then processed to make adetermination as to the presence of a moving body. An alarm indicatingoutput signal can then be produced and forwarded to a monitoring system.

An alarm indicating output signal is generated if the signal amplitudeis higher than the “high-threshold” or is lower than the “low-threshold”and persists for certain time. In response thereto, a PIR alarmindicating output signal is emitted.

The principle of signal processing by using this method is illustratedin FIG. 2. An output signal 210 from a PIR-type sensor varies about asignal baseline 220. A high-threshold 230 and a low-threshold 240 arepre-established.

Relative to the PIR signal as shown, if ΔT1>ΔT_TH or ΔT2>ΔT_TH (ΔT_TH isthe pre-set time threshold), then the PIR detector is triggered, and analarm indicating signal is emitted.

Disadvantages of the above described method include, missing alarms dueto smaller output signals. Such signals might be generated, for example,by an intruder wearing protective clothing, thick clothes, or using anumbrella to block infrared emissions. In other circumstance, it is easyto trigger false alarms for burst signals, such as these signalsgenerated by a sudden shock, a jarring, or a burst hardware inference.

In summary, in known PIR-type detectors, the output signals fromPIR-type sensors are indicative of sensed movement of heat sources inthe region being monitored. For example, intruder speed, height, weight,dress, behavior, posture, and temperature variations contribute togenerating signal waveforms with complex characteristics which result indifficulty in making accurate alarm determinations. This in turnproduces undesirable failures to properly emit alarm signals, or theemission of undesirable false alarms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art detector;

FIG. 2 is a graph illustrating PIR output signal variations over time;

FIG. 3 is a block diagram of a detector in accordance herewith;

FIG. 4 illustrates aspects of a method in accordance herewith;

FIG. 5 illustrates additional aspects of the method of FIG. 4;

FIG. 6 a flow diagram of a processing method in accordance herewith; and

FIG. 7 a flow diagram of an alternate processing method in accordanceherewith.

DETAILED DESCRIPTION

While disclosed embodiments can take many different forms, specificembodiments thereof are shown in the drawings and will be describedherein in detail with the understanding that the present disclosure isto be considered as an exemplification of the principles thereof as wellas the best mode of practicing same, and is not intended to limit theapplication or claims to the specific embodiment illustrated.

Apparatus and methods in accordance herewith are more effective inmaking alarm determinations in the presence of smaller sensor outputsignals than prior art processing. Additionally, false alarms areeliminated to a greater extent than in known PIR-type detectors. Inembodiments disclosed herein, energy associated with an incoming PIRsignal is evaluated. Results of that evaluation are used to make analarm determination.

FIG. 3 is a block diagram of a detector, or, apparatus 140 in accordanceherewith. Detector 140 includes a housing 140 a which carries a PIR-typesensor 150 physically configured to monitor an adjacent, external,region R. Output signals from the sensor 150, via line 150 a are coupledto analog shaping/amplifying processing signals 160.

Processed analog signals, via line 160 a are coupled tocontrol/processing circuits 170. Circuits 170 can be implemented, inpart, by one or more of analog input circuitry coupled to ananalog-to-digital converter, in combination with analog or digitalcircuitry to evaluate an energy parameter of the received signals fromthe sensor 150.

The evaluating circuitry 170 a can be implemented with analog circuits,digital signal processors, or general purpose programmable processorsall without limitation. In response to the presence of an alarm signal,from the circuitry 170 a, output circuitry 170 b can produce a localalarm indicating audible or visual signal, via device(s) 170 c.Additionally, an alarm indicating signal can be transmitted, via a wiredor wireless medium, to one or more displaced monitoring systems S.

FIG. 4 illustrates aspects of alarm determination processing which canbe carried out via the evaluating circuitry 170 a in response toreceived sensor signals 510, on line 160 a. A signal baseline 520, asample interval, or, control time 530, and various areas S1 540, S2 550,S3 560 are illustrated. In addition, a threshold S_TH can bepre-established and used to determine whether there an alarm signalshould be generated.

The signal baseline 520 is the reference of PIR signal. In a staticstate, the detecting signal 510 has a value that is close or same asthis baseline signal. The sample interval 530 is a time interval, presetaccording to a specific application, for controlling the sensitivity ofthe alarm trigger.

The various areas S1 540, S2 550, S3 560, of signal 510, and, the numberof such regions are determined by the characteristics of the signal(within the sample time ΔT 530). The physical significance of an area isthat it corresponds to an amount of energy received during the sampleinterval. Hence, the received PIR signal 510 can be analyzed based onthe amount of received energy associated with the signal.

Based on the energy in the signal 510, represented by the areas S1 . . .S3, various signal processing methods can be used to determine if analarm should be generated.

One form of processing corresponds to digital integration of the signal510 during the sample interval 530.

In a preset time ΔT, calculate S=|S1|+|S2|+|S3|+ . . . if S>S_TH, thenthe PIR energy is enough to meet the alarm trigger conditions, whereinthe S_TH is the area threshold preset, which controls the sensitivity ofthe alarm trigger. An example is used to illustrate how to use this“digital integration” method to calculate the area S1 (shown in FIG. 4).The method is shown in FIG. 5, wherein the region S1 is divided into 8parts (smaller rectangles), the associated time interval is ΔT1, signalbaseline is B0, and the calculating process is as follows:

The area of S1 is: S1=|S11|+|S12|+|S13|+|S14|+|S15|+|S16|+|S17|+|S18|

Wherein:

The area of S11 is: S11=(T11−T10)×[(V10+V11)÷2−B0]=ΔT1×[(V10+V11)÷2−B0]

The area of S12 is: S12=ΔT1×[(V12+V11)÷2−B0]

The area of S13 is: S13=ΔT1×[(V13+V12)÷2−B0]

The area of S14 is: S14=ΔT1×[(V14+V13)÷2−B0]

The area of S15 is: S15=ΔT1×[(V15+V14)÷2−B0]

The area of S16 is: S16=ΔT1×[(V16+V15)÷2−B0]

The area of S17 is: S17=ΔT1×[(V17+V16)÷2−B0]

The area of S18 is: S18=ΔT1×[(V18+V17)÷2−B0]

Then,

$\begin{matrix}{{S\; 1} = {{{S\; 11}} + {{S\; 12}} + {{S\; 13}} + {{S\; 14}} + {{S\; 15}} + {{S\; 16}} + {{S\; 17}} + {{S\; 18}}}} \\{= {\Delta \; T\; 1 \times \begin{bmatrix}{{\left( {{V\; 10} + {V\; 18}}\; \right) \div 2} + {V\; 11} + {V\; 12} + {V\; 13} +} \\{{V\; 14} + {V\; 15} + {V\; 16} + {V\; 17} - {8B\; 0}}\end{bmatrix}}}\end{matrix}$

So,

The first block area is:

${S\; 1} = {\sum\limits_{i = 1}^{8}\; {{S\; 1i}}}$

The total of area is:

$\begin{matrix}{S = {\sum\limits_{k = 1}^{n}\; {{S\; k}}}} \\{= {\sum\limits_{k = 1}^{n}\; {\sum\limits_{i = 1}^{m}\; {{S\; k\; i}}}}}\end{matrix}$

Wherein the “n” is the number of all area blocks in the time ΔT, and the“m” is number of parts of each area block divided, which is decided bythe size of different area block.

In summary, the above process can be applied to each of the regions S2,S3. The indicia of energy associated with each of the regions can thenbe summed. The result can be compared to the pre-determined thresholdS_TH to determine if an alarm should be generated.

Alternately, an amplitude oriented method can be used. In this regard,in a preset time interval ΔT, calculate V=|S1|+|S2|+|S3|+ . . . IfV>V_TH, then the PIR energy is enough to meet the alarm triggerconditions, wherein the V_TH is the voltage threshold preset, whichcontrols the sensitivity of the alarm trigger. FIG. 5 illustrates themethod. A plurality of differences can be established.

ΔV11=V11−B0, ΔV12=V12−B0, ΔV13=V13−B0, ΔV14=V14−B0,

ΔV15=V15−B0, ΔV16=V16−B0, ΔV17=V17−B0, ΔV18=V18−B0.

Then,

ΔV1=|ΔV11|+|ΔV12|+|ΔV13|+ΔV14|+|ΔV15|+|ΔV16|+|ΔV17|+|ΔV18|

ΔV1=(V11+V12+V13+V14+V15+V16+V17+V18)−8B0.

So,

The first part accumulation of voltage differences is:

${\Delta \; V\; 1} = {\sum\limits_{i = 1}^{8}\; {{\Delta \; V\; 1\; i}}}$

The total accumulation of voltage differences for all segments, such asS1 . . . S3, is:

$\begin{matrix}{V = {\sum\limits_{k = 1}^{n}\; {{\Delta \; V\; k}}}} \\{= {\sum\limits_{k = 1}^{n}\; {\sum\limits_{i = 1}^{m}\; {{V\; k\; i}}}}}\end{matrix}$

Wherein the “n” is the number of all parts (including the differencethat voltage is above or below the baseline) in the time ΔT, and the “m”is the number of the difference of each part, which is decided by thesize of different part. This result can be compared to a predeterminedalarm threshold to make an alarm determination.

FIGS. 6, 7 illustrate additional aspects of the above describedprocessing. With respect to the flow diagram of process 700, FIG. 6, adetector can be initialized as at 710. The PIR signal values over thesample interval 530 can be acquired as at 720. The areas, such as S1 . .. S3 can be established, as described above, as at 730. The total areaassociated with the curve 510 can be determined as at 740. Adetermination can be made as to whether the sum exceeded thepredetermined alarm threshold, as at 750. If so, an alarm can betriggered, as at 760. Otherwise, the next sample can be identified, asat 755.

FIG. 7, illustrates processing 800 which relates to the alternate“voltage accumulation” method discussed above. A detector can beinitialized as at 810. The values of the respective sensor outputsignals, such as 510, can be acquired during the sample interval 530, asat 820.

The difference values can then be determined, as at 830. A total energyrelated parameter value can be determined as at 840. A comparison can bemade with the pre-determined alarm threshold, as at 850. If not, thenext sample can be defined to be acquired, as at 855. Alternately, as at860, a times triggered count can be incremented. The total times analarm condition has been indicated is compared to a threshold, as at870. If exceeded, an alarm can be triggered, as at 880. Otherwise thenext sample can be defined and acquired, as at 875.

Those of skill will understand that the above disclosure is exemplaryonly. Different numbers of sample points, or sample intervals all comewithin the spirit and scope hereof.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.Further, logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. Other steps may be provided, or steps may be eliminated, fromthe described flows, and other components may be add to, or removed fromthe described embodiments.

1. A motion detector comprising: an infrared sensor, the sensor having afield of view and an output port and generating a signal at the outputport; and circuitry to receive and to process the signal to establish anenergy parameter value associated with the signal.
 2. A detector as inclaim 1 which includes circuitry to detect if the processed signalindicates that a moving body has been sensed in the field of view.
 3. Adetector as in claim 2 which includes circuitry to carry out one of ananalog signal processing function, or, a digital signal processingfunction.
 4. A detector as in claim 3 where the circuitry is selectedfrom a class which includes at least operational amplifiers, digitalsignal processors, and programmable general purpose processors.
 5. Adetector as in claim 2 where the circuitry is selected from a classwhich includes at least operational amplifiers, digital signalprocessors, and programmable general purpose processors.
 6. A detectoras in claim 1 where the circuitry to establish the energy parametervalue accumulates energy related indicia from the signal.
 7. A detectoras in claim 6 where the energy related indicia comprises one ofintegrated values, or changes in signal amplitude values.
 8. A detectoras in claim 7 which includes circuitry to carry out one of an analogsignal processing function, or, a digital signal processing function. 9.A detector as in claim 8 where the circuitry is selected from a classwhich includes at least operational amplifiers, digital signalprocessors, and programmable general purpose processors.
 10. A detectoras in claim 1 where the circuitry processes the signals and establishes,during a plurality of predetermined time intervals, respective energyparameter values.
 11. A detector as in claim 9 where the circuitryprocesses the signals and establishes, during a plurality ofpredetermined time intervals, respective energy parameter values.
 12. Amethod of monitoring a region comprising: obtaining potential movementrelated signals from a region being monitored; establishing at least onesample time interval; evaluating energy related characteristics of thesignal during at least one sample interval; and determining if theevaluated energy related characteristic is indicative of movement in theregion.
 13. A method as in claim 12 where determining includes comparingthe evaluated energy related characteristic to a pre-determinedthreshold.
 14. A method as in claim 12 where evaluating includesaccumulating the energy related characteristics of the signal.
 15. Amethod as in claim 14 where accumulating includes at least one ofintegrating or forming a plurality of differential signal values.